(1) Field of the Invention
This invention relates to a method for correcting measurement errors due to radial runout of rims and/or of a load wheel in a tire uniformity inspecting machine.
(2) Description of the Prior Art
In tire uniformity inspecting machines, the uniformity of a tire is inspected by measuring variations in the reaction force of a tire as imposed on the circumferential surface of a load wheel which is maintained at a constant distance from the center of tire-supporting rims. However, it is often the case that the measured values contain errors due to rotational deflections of the rims which grip the inspecting tire and/or of the load wheel. For example, if a rim with a rotational deflection of 25 microns is used for the inspection of a tire with a spring constant of 20 kgf/mm, the measured RFV (radial force variation) contains an error of 0.5 kgf which is a value obtained by multiplying the amount of radial runout by the spring constant. Recently, tires have been considerably improved in the value of uniformity and usually are required to have a RFV value smaller than 10 kgf, in some cases a RFV value of 8 kgf or 5 kgf. Therefore, the error component of 0.5 kgf in such a small RFV value is unignorable and should be suppressed to a minimum. Of course, the rotational component parts of the tire uniformity inspecting machines are manufactured with an extremely high precision, including the upper and lower rims, the mechanism for rotating the rims, and the load wheel. However, as a matter of fact, it is impossible to make zero the deflections of the machined rotational component parts partly because of technical difficulties and partly because of uneconomically large expenses involved in the machining operations. In addition, small deflections also occur due to deteriorations of the rotational component parts or due to rust or bruises which are developed on the tire retaining portions during use of the inspecting machines. Even if the rotational component parts are fabricated with an accuracy on the order of 10 microns as unit bodies, a radial runout builds up to a value on the order of 20 microns and are developed when they are assembled. Since complete elimination of the rotational defections of the rims and load wheels is difficult, it is more practical to accept a certain degree of deflections and to correct errors of measurement due to deflections of rims and/or a load wheel by subtracting influences of rotational deflections from measured values.